/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.base;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.regex.Pattern;

/**
 * Extracts non-overlapping substrings from an input string, typically by recognizing appearances of
 * a <i>separator</i> sequence. This separator can be specified as a single {@linkplain #on(char)
 * character}, fixed {@linkplain #on(String) string}, {@linkplain #onPattern regular expression} or
 * {@link #on(CharMatcher) CharMatcher} instance. Or, instead of using a separator at all, a
 * splitter can extract adjacent substrings of a given {@linkplain #fixedLength fixed length}.
 *
 * <p>
 * For example, this expression:
 * 
 * <pre>
 *    {@code
 *
 *   Splitter.on(',').split("foo,bar,qux")}
 * </pre>
 *
 * ... produces an {@code Iterable} containing {@code "foo"}, {@code "bar"} and {@code "qux"}, in
 * that order.
 *
 * <p>
 * By default, {@code Splitter}'s behavior is simplistic and unassuming. The following expression:
 * 
 * <pre>
 *    {@code
 *
 *   Splitter.on(',').split(" foo,,,  bar ,")}
 * </pre>
 *
 * ... yields the substrings {@code [" foo", "", "", "  bar ", ""]}. If this is not the desired
 * behavior, use configuration methods to obtain a <i>new</i> splitter instance with modified
 * behavior:
 * 
 * <pre>
 * {
 *     &#64;code
 *
 *     private static final Splitter MY_SPLITTER = Splitter.on(',').trimResults().omitEmptyStrings();
 * }
 * </pre>
 *
 * <p>
 * Now {@code MY_SPLITTER.split("foo,,,  bar ,")} returns just {@code ["foo",
 * "bar"]}. Note that the order in which these configuration methods are called is never
 * significant.
 *
 * <p>
 * <b>Warning:</b> Splitter instances are immutable. Invoking a configuration method has no effect
 * on the receiving instance; you must store and use the new splitter instance it returns instead.
 * 
 * <pre>
 * {
 *     &#64;code
 *
 *     // Do NOT do this
 *     Splitter splitter = Splitter.on('/');
 *     splitter.trimResults(); // does nothing!
 *     return splitter.split("wrong / wrong / wrong");
 * }
 * </pre>
 *
 * <p>
 * For separator-based splitters that do not use {@code omitEmptyStrings}, an input string
 * containing {@code n} occurrences of the separator naturally yields an iterable of size
 * {@code n + 1}. So if the separator does not occur anywhere in the input, a single substring is
 * returned containing the entire input. Consequently, all splitters split the empty string to
 * {@code [""]} (note: even fixed-length splitters).
 *
 * <p>
 * Splitter instances are thread-safe immutable, and are therefore safe to store as
 * {@code static final} constants.
 *
 * <p>
 * The {@link Joiner} class provides the inverse operation to splitting, but note that a round-trip
 * between the two should be assumed to be lossy.
 *
 * <p>
 * See the Guava User Guide article on
 * <a href="https://github.com/google/guava/wiki/StringsExplained#splitter">{@code Splitter}</a>.
 *
 * @author Julien Silland
 * @author Jesse Wilson
 * @author Kevin Bourrillion
 * @author Louis Wasserman
 * @since 1.0
 */
@GwtCompatible(emulated = true)
public final class Splitter {
    private final CharMatcher trimmer;
    private final boolean omitEmptyStrings;
    private final Strategy strategy;
    private final int limit;

    private Splitter(Strategy strategy) {
        this(strategy, false, CharMatcher.none(), Integer.MAX_VALUE);
    }

    private Splitter(Strategy strategy, boolean omitEmptyStrings, CharMatcher trimmer, int limit) {
        this.strategy = strategy;
        this.omitEmptyStrings = omitEmptyStrings;
        this.trimmer = trimmer;
        this.limit = limit;
    }

    /**
     * Returns a splitter that uses the given single-character separator. For example,
     * {@code Splitter.on(',').split("foo,,bar")} returns an iterable containing
     * {@code ["foo", "", "bar"]}.
     *
     * @param separator the character to recognize as a separator
     * @return a splitter, with default settings, that recognizes that separator
     */
    public static Splitter on(char separator) {
        return on(CharMatcher.is(separator));
    }

    /**
     * Returns a splitter that considers any single character matched by the given
     * {@code CharMatcher} to be a separator. For example, {@code
     * Splitter.on(CharMatcher.anyOf(";,")).split("foo,;bar,quux")} returns an iterable containing
     * {@code ["foo", "", "bar", "quux"]}.
     *
     * @param separatorMatcher a {@link CharMatcher} that determines whether a character is a
     *        separator
     * @return a splitter, with default settings, that uses this matcher
     */
    public static Splitter on(final CharMatcher separatorMatcher) {
        checkNotNull(separatorMatcher);

        return new Splitter(new Strategy() {
            @Override
            public SplittingIterator iterator(Splitter splitter, final CharSequence toSplit) {
                return new SplittingIterator(splitter, toSplit) {
                    @Override
                    int separatorStart(int start) {
                        return separatorMatcher.indexIn(toSplit, start);
                    }

                    @Override
                    int separatorEnd(int separatorPosition) {
                        return separatorPosition + 1;
                    }
                };
            }
        });
    }

    /**
     * Returns a splitter that uses the given fixed string as a separator. For example,
     * {@code Splitter.on(", ").split("foo, bar,baz")} returns an iterable containing
     * {@code ["foo", "bar,baz"]}.
     *
     * @param separator the literal, nonempty string to recognize as a separator
     * @return a splitter, with default settings, that recognizes that separator
     */
    public static Splitter on(final String separator) {
        checkArgument(separator.length() != 0, "The separator may not be the empty string.");
        if (separator.length() == 1) {
            return Splitter.on(separator.charAt(0));
        }
        return new Splitter(new Strategy() {
            @Override
            public SplittingIterator iterator(Splitter splitter, CharSequence toSplit) {
                return new SplittingIterator(splitter, toSplit) {
                    @Override
                    public int separatorStart(int start) {
                        int separatorLength = separator.length();

                        positions: for (int p = start, last = toSplit.length() - separatorLength; p <= last; p++) {
                            for (int i = 0; i < separatorLength; i++) {
                                if (toSplit.charAt(i + p) != separator.charAt(i)) {
                                    continue positions;
                                }
                            }
                            return p;
                        }
                        return -1;
                    }

                    @Override
                    public int separatorEnd(int separatorPosition) {
                        return separatorPosition + separator.length();
                    }
                };
            }
        });
    }

    /**
     * Returns a splitter that considers any subsequence matching {@code pattern} to be a separator.
     * For example, {@code Splitter.on(Pattern.compile("\r?\n")).split(entireFile)} splits a string
     * into lines whether it uses DOS-style or UNIX-style line terminators.
     *
     * @param separatorPattern the pattern that determines whether a subsequence is a separator.
     *        This pattern may not match the empty string.
     * @return a splitter, with default settings, that uses this pattern
     * @throws IllegalArgumentException if {@code separatorPattern} matches the empty string
     */
    @GwtIncompatible // java.util.regex
    public static Splitter on(Pattern separatorPattern) {
        return on(new JdkPattern(separatorPattern));
    }

    private static Splitter on(final CommonPattern separatorPattern) {
        checkArgument(!separatorPattern.matcher("").matches(), "The pattern may not match the empty string: %s",
                separatorPattern);

        return new Splitter(new Strategy() {
            @Override
            public SplittingIterator iterator(final Splitter splitter, CharSequence toSplit) {
                final CommonMatcher matcher = separatorPattern.matcher(toSplit);
                return new SplittingIterator(splitter, toSplit) {
                    @Override
                    public int separatorStart(int start) {
                        return matcher.find(start) ? matcher.start() : -1;
                    }

                    @Override
                    public int separatorEnd(int separatorPosition) {
                        return matcher.end();
                    }
                };
            }
        });
    }

    /**
     * Returns a splitter that considers any subsequence matching a given pattern (regular
     * expression) to be a separator. For example,
     * {@code Splitter.onPattern("\r?\n").split(entireFile)} splits a string into lines whether it
     * uses DOS-style or UNIX-style line terminators. This is equivalent to
     * {@code Splitter.on(Pattern.compile(pattern))}.
     *
     * @param separatorPattern the pattern that determines whether a subsequence is a separator.
     *        This pattern may not match the empty string.
     * @return a splitter, with default settings, that uses this pattern
     * @throws IllegalArgumentException if {@code separatorPattern} matches the empty string or is a
     *         malformed expression
     */
    @GwtIncompatible // java.util.regex
    public static Splitter onPattern(String separatorPattern) {
        return on(Platform.compilePattern(separatorPattern));
    }

    /**
     * Returns a splitter that divides strings into pieces of the given length. For example,
     * {@code Splitter.fixedLength(2).split("abcde")} returns an iterable containing
     * {@code ["ab", "cd", "e"]}. The last piece can be smaller than {@code length} but will never
     * be empty.
     *
     * <p>
     * <b>Exception:</b> for consistency with separator-based splitters, {@code
     * split("")} does not yield an empty iterable, but an iterable containing {@code ""}. This is
     * the only case in which {@code
     * Iterables.size(split(input))} does not equal {@code
     * IntMath.divide(input.length(), length, CEILING)}. To avoid this behavior, use
     * {@code omitEmptyStrings}.
     *
     * @param length the desired length of pieces after splitting, a positive integer
     * @return a splitter, with default settings, that can split into fixed sized pieces
     * @throws IllegalArgumentException if {@code length} is zero or negative
     */
    public static Splitter fixedLength(final int length) {
        checkArgument(length > 0, "The length may not be less than 1");

        return new Splitter(new Strategy() {
            @Override
            public SplittingIterator iterator(final Splitter splitter, CharSequence toSplit) {
                return new SplittingIterator(splitter, toSplit) {
                    @Override
                    public int separatorStart(int start) {
                        int nextChunkStart = start + length;
                        return (nextChunkStart < toSplit.length() ? nextChunkStart : -1);
                    }

                    @Override
                    public int separatorEnd(int separatorPosition) {
                        return separatorPosition;
                    }
                };
            }
        });
    }

    /**
     * Returns a splitter that behaves equivalently to {@code this} splitter, but automatically
     * omits empty strings from the results. For example, {@code
     * Splitter.on(',').omitEmptyStrings().split(",a,,,b,c,,")} returns an iterable containing only
     * {@code ["a", "b", "c"]}.
     *
     * <p>
     * If either {@code trimResults} option is also specified when creating a splitter, that
     * splitter always trims results first before checking for emptiness. So, for example, {@code
     * Splitter.on(':').omitEmptyStrings().trimResults().split(": : : ")} returns an empty iterable.
     *
     * <p>
     * Note that it is ordinarily not possible for {@link #split(CharSequence)} to return an empty
     * iterable, but when using this option, it can (if the input sequence consists of nothing but
     * separators).
     *
     * @return a splitter with the desired configuration
     */
    public Splitter omitEmptyStrings() {
        return new Splitter(strategy, true, trimmer, limit);
    }

    /**
     * Returns a splitter that behaves equivalently to {@code this} splitter but stops splitting
     * after it reaches the limit. The limit defines the maximum number of items returned by the
     * iterator, or the maximum size of the list returned by {@link #splitToList}.
     *
     * <p>
     * For example, {@code Splitter.on(',').limit(3).split("a,b,c,d")} returns an iterable
     * containing {@code ["a", "b", "c,d"]}. When omitting empty strings, the omitted strings do not
     * count. Hence, {@code Splitter.on(',').limit(3).omitEmptyStrings().split("a,,,b,,,c,d")}
     * returns an iterable containing {@code ["a", "b", "c,d"}. When trim is requested, all entries
     * are trimmed, including the last. Hence
     * {@code Splitter.on(',').limit(3).trimResults().split(" a , b , c , d ")} results in
     * {@code ["a", "b", "c , d"]}.
     *
     * @param limit the maximum number of items returned
     * @return a splitter with the desired configuration
     * @since 9.0
     */
    public Splitter limit(int limit) {
        checkArgument(limit > 0, "must be greater than zero: %s", limit);
        return new Splitter(strategy, omitEmptyStrings, trimmer, limit);
    }

    /**
     * Returns a splitter that behaves equivalently to {@code this} splitter, but automatically
     * removes leading and trailing {@linkplain CharMatcher#whitespace whitespace} from each
     * returned substring; equivalent to {@code trimResults(CharMatcher.whitespace())}. For example,
     * {@code
     * Splitter.on(',').trimResults().split(" a, b ,c ")} returns an iterable containing
     * {@code ["a", "b", "c"]}.
     *
     * @return a splitter with the desired configuration
     */
    public Splitter trimResults() {
        return trimResults(CharMatcher.whitespace());
    }

    /**
     * Returns a splitter that behaves equivalently to {@code this} splitter, but removes all
     * leading or trailing characters matching the given {@code
     * CharMatcher} from each returned substring. For example, {@code
     * Splitter.on(',').trimResults(CharMatcher.is('_')).split("_a ,_b_ ,c__")} returns an iterable
     * containing {@code ["a ", "b_ ", "c"]}.
     *
     * @param trimmer a {@link CharMatcher} that determines whether a character should be removed
     *        from the beginning/end of a subsequence
     * @return a splitter with the desired configuration
     */
    // TODO(kevinb): throw if a trimmer was already specified!
    public Splitter trimResults(CharMatcher trimmer) {
        checkNotNull(trimmer);
        return new Splitter(strategy, omitEmptyStrings, trimmer, limit);
    }

    /**
     * Splits {@code sequence} into string components and makes them available through an
     * {@link Iterator}, which may be lazily evaluated. If you want an eagerly computed
     * {@link List}, use {@link #splitToList(CharSequence)}.
     *
     * @param sequence the sequence of characters to split
     * @return an iteration over the segments split from the parameter.
     */
    public Iterable<String> split(final CharSequence sequence) {
        checkNotNull(sequence);

        return new Iterable<String>() {
            @Override
            public Iterator<String> iterator() {
                return splittingIterator(sequence);
            }

            @Override
            public String toString() {
                return Joiner.on(", ").appendTo(new StringBuilder().append('['), this).append(']').toString();
            }
        };
    }

    private Iterator<String> splittingIterator(CharSequence sequence) {
        return strategy.iterator(this, sequence);
    }

    /**
     * Splits {@code sequence} into string components and returns them as an immutable list. If you
     * want an {@link Iterable} which may be lazily evaluated, use {@link #split(CharSequence)}.
     *
     * @param sequence the sequence of characters to split
     * @return an immutable list of the segments split from the parameter
     * @since 15.0
     */
    @Beta
    public List<String> splitToList(CharSequence sequence) {
        checkNotNull(sequence);

        Iterator<String> iterator = splittingIterator(sequence);
        List<String> result = new ArrayList<String>();

        while (iterator.hasNext()) {
            result.add(iterator.next());
        }

        return Collections.unmodifiableList(result);
    }

    /**
     * Returns a {@code MapSplitter} which splits entries based on this splitter, and splits entries
     * into keys and values using the specified separator.
     *
     * @since 10.0
     */
    @Beta
    public MapSplitter withKeyValueSeparator(String separator) {
        return withKeyValueSeparator(on(separator));
    }

    /**
     * Returns a {@code MapSplitter} which splits entries based on this splitter, and splits entries
     * into keys and values using the specified separator.
     *
     * @since 14.0
     */
    @Beta
    public MapSplitter withKeyValueSeparator(char separator) {
        return withKeyValueSeparator(on(separator));
    }

    /**
     * Returns a {@code MapSplitter} which splits entries based on this splitter, and splits entries
     * into keys and values using the specified key-value splitter.
     *
     * @since 10.0
     */
    @Beta
    public MapSplitter withKeyValueSeparator(Splitter keyValueSplitter) {
        return new MapSplitter(this, keyValueSplitter);
    }

    /**
     * An object that splits strings into maps as {@code Splitter} splits iterables and lists. Like
     * {@code Splitter}, it is thread-safe and immutable.
     *
     * @since 10.0
     */
    @Beta
    public static final class MapSplitter {
        private static final String INVALID_ENTRY_MESSAGE = "Chunk [%s] is not a valid entry";
        private final Splitter outerSplitter;
        private final Splitter entrySplitter;

        private MapSplitter(Splitter outerSplitter, Splitter entrySplitter) {
            this.outerSplitter = outerSplitter; // only "this" is passed
            this.entrySplitter = checkNotNull(entrySplitter);
        }

        /**
         * Splits {@code sequence} into substrings, splits each substring into an entry, and returns
         * an unmodifiable map with each of the entries. For example,
         * {@code Splitter.on(';').trimResults().withKeyValueSeparator("=>").split("a=>b ; c=>b")}
         * will return a mapping from {@code "a"} to {@code "b"} and {@code "c"} to {@code "b"}.
         *
         * <p>
         * The returned map preserves the order of the entries from {@code sequence}.
         *
         * @throws IllegalArgumentException if the specified sequence does not split into valid map
         *         entries, or if there are duplicate keys
         */
        public Map<String, String> split(CharSequence sequence) {
            Map<String, String> map = new LinkedHashMap<String, String>();
            for (String entry : outerSplitter.split(sequence)) {
                Iterator<String> entryFields = entrySplitter.splittingIterator(entry);

                checkArgument(entryFields.hasNext(), INVALID_ENTRY_MESSAGE, entry);
                String key = entryFields.next();
                checkArgument(!map.containsKey(key), "Duplicate key [%s] found.", key);

                checkArgument(entryFields.hasNext(), INVALID_ENTRY_MESSAGE, entry);
                String value = entryFields.next();
                map.put(key, value);

                checkArgument(!entryFields.hasNext(), INVALID_ENTRY_MESSAGE, entry);
            }
            return Collections.unmodifiableMap(map);
        }
    }

    private interface Strategy {
        Iterator<String> iterator(Splitter splitter, CharSequence toSplit);
    }

    private abstract static class SplittingIterator extends AbstractIterator<String> {
        final CharSequence toSplit;
        final CharMatcher trimmer;
        final boolean omitEmptyStrings;

        /**
         * Returns the first index in {@code toSplit} at or after {@code start} that contains the
         * separator.
         */
        abstract int separatorStart(int start);

        /**
         * Returns the first index in {@code toSplit} after {@code
         * separatorPosition} that does not contain a separator. This method is only invoked after a
         * call to {@code separatorStart}.
         */
        abstract int separatorEnd(int separatorPosition);

        int offset = 0;
        int limit;

        protected SplittingIterator(Splitter splitter, CharSequence toSplit) {
            this.trimmer = splitter.trimmer;
            this.omitEmptyStrings = splitter.omitEmptyStrings;
            this.limit = splitter.limit;
            this.toSplit = toSplit;
        }

        @Override
        protected String computeNext() {
            /*
             * The returned string will be from the end of the last match to the beginning of the
             * next one. nextStart is the start position of the returned substring, while offset is
             * the place to start looking for a separator.
             */
            int nextStart = offset;
            while (offset != -1) {
                int start = nextStart;
                int end;

                int separatorPosition = separatorStart(offset);
                if (separatorPosition == -1) {
                    end = toSplit.length();
                    offset = -1;
                } else {
                    end = separatorPosition;
                    offset = separatorEnd(separatorPosition);
                }
                if (offset == nextStart) {
                    /*
                     * This occurs when some pattern has an empty match, even if it doesn't match
                     * the empty string -- for example, if it requires lookahead or the like. The
                     * offset must be increased to look for separators beyond this point, without
                     * changing the start position of the next returned substring -- so nextStart
                     * stays the same.
                     */
                    offset++;
                    if (offset > toSplit.length()) {
                        offset = -1;
                    }
                    continue;
                }

                while (start < end && trimmer.matches(toSplit.charAt(start))) {
                    start++;
                }
                while (end > start && trimmer.matches(toSplit.charAt(end - 1))) {
                    end--;
                }

                if (omitEmptyStrings && start == end) {
                    // Don't include the (unused) separator in next split string.
                    nextStart = offset;
                    continue;
                }

                if (limit == 1) {
                    // The limit has been reached, return the rest of the string as the
                    // final item. This is tested after empty string removal so that
                    // empty strings do not count towards the limit.
                    end = toSplit.length();
                    offset = -1;
                    // Since we may have changed the end, we need to trim it again.
                    while (end > start && trimmer.matches(toSplit.charAt(end - 1))) {
                        end--;
                    }
                } else {
                    limit--;
                }

                return toSplit.subSequence(start, end).toString();
            }
            return endOfData();
        }
    }
}
